1. Field of the Invention
The present invention relates to a cylindrical secondary battery, more particularly, to a secondary battery wherein an insulating gasket prevents an inner short circuit between a cylindrical can and a cap assembly thus further prevents an inner short circuit generated by external factors between a cylindrical can and a cap assembly.
2. Description of the Related Art
Recently, compact and lightweight electric/electronic apparatuses such as mobile phones, notebook computers, personal digital assistants (PDA), digital cameras have been developed and manufactured. Such portable electric/electronic apparatuses employ a battery pack in order to operate in the places where no external power supply is equipped, and the battery pack has at least one battery inside so as to output a predetermined voltage for driving portable electric/electronic apparatuses for a certain period of time.
The recent trend of battery pack is to employ a chargeable/dischargeable secondary battery which is economically advantageous. The secondary battery for the battery pack typically includes a nickel-cadmium battery, a nickel-hydrogen battery and a lithium rechargeable battery.
The lithium rechargeable battery has an operating voltage of 3.6V which is three times higher than the nickel-cadmium battery and the nickel-hydrogen battery which are widely used as power supplies for portable electric/electronic apparatuses. Because energy density per unit weight of the lithium rechargeable battery is high, its usage is expended.
The lithium rechargeable battery employs a lithium-based oxide as a positive electrode active material and a carbon material as a negative electrode active material. Generally, the lithium rechargeable battery can be classified into a liquid electrolyte battery and a polymer electrolyte battery according to different kinds of electrolytes. The lithium rechargeable battery using a liquid electrolyte is called as a lithium ion battery, and a lithium rechargeable battery using a polymer electrolyte is called as a lithium polymer battery. Furthermore, the lithium rechargeable battery may be formed in various shapes, and the typical shape is a cylindrical shape, a rectangular shape and a pouch shape.
The lithium rechargeable batteries which are formed in various shapes as stated above, the structure of a cylindrical lithium rechargeable battery will be briefly explained as follows. Hereinafter, the cylindrical lithium battery is referred to as the cylindrical rechargeable battery.
The cylindrical rechargeable battery includes a jelly-roll type electrode assembly, a cylindrical can receiving the electrode assembly, and a cap assembly connected to the open side of the cylindrical can.
The electrode assembly includes a positive electrode plate, a negative electrode plate, and a separator. A positive electrode plate and a negative electrode plate are stacked and a separator is interposed therebetween. The positive electrode, negative electrode plates and the separator are wound together in one direction thus the electrode assembly is formed in a jelly-roll type structure. A positive electrode tab and a negative electrode tab are attached to the positive electrode plate and the negative electrode plate respectively.
The cylindrical can receives the electrode assembly, and the electrode assembly has insulating plates mounted on the upper and lower part thereof respectively.
The cap assembly seals the open side of the cylindrical can, and the cap assembly includes a electrode cap, PTC (Positive Temperature Coefficient) elements, and a safety vent.
A gasket is mounted along the outer circumference of the cap assembly and the gasket insulates the cap assembly and the cylindrical can.
A ring type washer is mounted between the cylindrical can and the electrode cap to prevent a short circuit generated by external factors between the cylindrical can and the electrode cap. For example, when a conductive material having a thin thickness such as an electric wire is accidently inserted between the cylindrical can and the electrode cap, a short circuit of the battery occurs. The washer made of an electrical insulating material fills the gap between the cylindrical can and the electrode cap, thus prevents any electrical contact between the cylindrical can and the electrode cap Therefore, the washer made of an electrical insulating material is employed to mount between the cylindrical can and the electrode cap to prevent a short circuit generated by external factors between the cylindrical can and the electrode cap.
The washer is mounted between the cylindrical can and the electrode cap during the fabrication step of completing the cylindrical rechargeable battery, and the fabrication of the cylindrical rechargeable battery is completed by tubing the battery with the washer placed between the cylindrical can and the electrode cap.
The conventional cylindrical rechargeable battery described above, however, employs an additional washer to prevent possible external factor induced short circuit, so the fabricating process of the cylindrical battery becomes more complicated because an additional process is needed to insert the washer into the cap assembly of the cylindrical rechargeable battery or into the cylindrical can.
Further, because the washer is not integrally manufactured with the battery, the washer may move away from its original position during the usage of the cylindrical rechargeable battery. If the washer moves away from its original position, the washer may not efficiently cut off the cylindrical can from the cap assembly, thus a gap between the cylindrical can and the cap assembly is generated. Thin conductive materials may be accidently inserted into the gap from outside of the battery, thereby resulting in a short circuit of the battery.